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November 18, 2013

Volcano Discovered Under Antarctic Ice

by VOA News

Scientists have discovered a previously unknown volcano buried a kilometer under the Antarctic ice.

A group of scientists from Washington University initially set out to study the history of Anarctica’s climate. To do so, they set up seismic equipment across Marie Byrd Land in West Anarctica to “weigh the ice.”

Two seismic events, one in January of 2010 and another in March of 2011, puzzled the team.

The events were weak and very low frequency, which strongly suggested they weren’t tectonic in origin. While low-magnitude seismic events of tectonic origin typically have frequencies of 10 to 20 cycles per second, this shaking was dominated by frequencies of 2 to 4 cycles per second.

Scientists still needed to know if events were the result of rock grinding on rock, ice groaning over ice, or, perhaps, hot gases and liquid rock forcing their way through cracks in a volcanic complex.

“I started seeing events that kept occurring at the same location, which was odd,” PhD student Amanda Lough said. “Then I realized they were close to some mountains, but not right on top of them.”

“My first thought was, ‘OK, maybe it’s just coincidence.’ But then I looked more closely and realized that the mountains were actually volcanoes and there was an age progression to the range. The volcanoes closest to the seismic events were the youngest ones.”

After analyzing the data more, the scientists determined the events had occurred at depths of 25 to 40 kilometers. This is extraordinarily deep - deep enough to be near the boundary between the Earth’s crust and mantle, called the Moho, and more or less rules out a glacial origin.

That information also casts doubt on a tectonic one. “A tectonic event might have a hypocenter 10 to 15 kilometers deep, but at 25 to 40 kilometers, these were way too deep,” Lough said.

The team also consulted radar produced topographic maps to look at the area.

“In these maps, you can see that there’s elevation in the bed topography at the same location as the seismic events,” Lough said.

The radar images also showed a layer of ash buried under the ice. “They see this layer all around our group of earthquakes and only in this area,” Lough said.

“Their best guess is that it came from Mount Waesche, an existing volcano near Mount Sidley. But that is also interesting because scientists had no idea when Mount Waesche was last active, and the ash layer sets the age of the eruption at 8,000 years ago.”

Scientists still have questions.

“Most mountains in Antarctica are not volcanic,” Wiens said, “but most in this area are. Is it because East and West Antarctica are slowly rifting apart? We don’t know exactly. But we think there is probably a hot spot in the mantle here producing magma far beneath the surface.”

Lough said the volcano will “definitely” erupt, but that for the eruption to break through the ice, it would need to release about 1,000 times more energy than the typical eruption.

Still, a subglacial eruption would melt a lot of ice, scientists said. This could create millions of gallons of water beneath the ice, which would rush toward the sea and feed into the hydrological catchment of the MacAyeal Ice Stream, one of several major ice streams draining ice from Marie Byrd Land into the Ross Ice Shelf.

By lubricating the bedrock, it will speed the flow of the overlying ice, perhaps increasing the rate of ice-mass loss in West Antarctica.

The discovery of the new as-yet-unnamed volcano is announced in the Nov. 17 advance online issue of Nature Geoscience.